Focal hypohidrosis in lesional skin in a probable case of confluent and reticulated papillomatosis: A case report with insight into the pathomechanism of recurrence.

Confluent and reticulated papillomatosis (CRP) is a rare skin disorder that develops in young adults and presents as persistent brown papules and plaques predominantly affecting the intertriginous areas, however, its etiopathogenesis remains elusive. Herein, we report a probable case of CRP with lesional hypohidrosis as detected by sweat test and provide insight into the pathomechanism. A 23-year-old man presented with nine-months history of painful sensation on his trunk without any skin change. The result of sweat test was compatible with acquired idiopathic generalized anhidrosis. Topical heparinoid and physical exercise improved the symptoms. However, he started to notice asymptomatic brownish reticulated macules on the trunk. Intriguingly, focal hypohidrosis, as detected by sweat test was evident on the macules. In histology, the lesional skin demonstrated hyperkeratosis, acanthosis, basal melanosis, mild papillomatosis, and obstruction of the sweat duct in the upper dermis, which were not observed in the peri-lesional skin. Accumulation of the sweat in the luminal aspect of the secretory portion and dilation of the sweat duct in the deeper dermis was detected in the lesional skin, as highlighted by anti-dermcidin staining. Aquaporin 5 expression in the secretory portion was more confined to the cell membrane in the lesional skin. Both brownish macules and lesional hypohidrosis simultaneously improved in summer and exacerbated in winter. Literature review found nine reports on recurrent CRP, and obesity was thought to be a major comorbidity in recurrent CRP cases. Obesity is often associated with sweat dysregulation. This, together with the findings in our case, implied the possible contribution of focal sweating abnormality in the pathogenesis of reticulated skin lesion in our case.